Answer:
- <u>First choice: 0.042</u>
Explanation:
Given decomposition reaction:
- 1PCl₅ (g) ⇄ 1PCl₃ + 1Cl₂(g)
Equilibrium constant:
Stoichiometric coefficients and powers equal to 1 are not usually shown as they are understood, but I included them in order to shwow you how they intervene in the equilibrium expressions: each concentration is raised to a power equal to the respective stoichiometric coefficient in the equilibrium equation.
So, your calculations are:

The percentage of Chromium in Chromium Oxide is calculated as follow,
Step 1: Calculate Molar mass of Cr₂O₃,
Cr = 51.99 u
O = 16 u
So,
2(51.99) + 3(16) = 103.98 + 48 = 151.98 u
Step 2: Secondly divide molar mass of only chromium with total mass of Cr₂O₃ and multiply with 100.
i.e.
=

× 100
=
68.41 %
So, the %age composition of chromium in chromium oxide is
68.41 %.
It's back wards lol you need to take it right